This invention relates to a four-stroke internal combustion engine for outboard motors and more particularly to an improved lubricating system for the four-stroke engine of an outboard motor.
Although most outboard motors operate on the two-stroke principle, there are some advantages to employing four-stroke engines in outboard motors. In connection with the use of an engine operating on the four-stroke principle, it is necessary to provide an oil reservoir in which the lubricating oil for the engine is contained. Since the motor is normally positioned with the crankshaft of the engine extending vertically, it has been the common practice to provide an oil reservoir for containing the lubricant at a level below the engine and below its crankcase. Oil may drain into this oil reservoir from the crankcase or from the camshaft chamber of the engine by gravity. In order to insure this gravity return, it is, of course, necessary to provide an opening through which the lubricant may return to the reservoir. However, even though the outboard motor is normally operated in a vertical position, there are many times when the motor is disposed horizontally, such as when being transported. When being transported, it is desirable to lay the motor on its forward face so that the lubricant cannot flow back from the reservoir into the engine. Such reverse flow could cause the lubricant to enter the exhaust system and contaminate the water or environment when the engine was next placed in an upright position. Although it has been proposed to prevent such reverse flow by using small openings and by carefully controlling the position of the opening, this expedient can retard the rate of flow of lubricant back to the reservoir during normal operating conditions and cause problems.
It is, therefore, a principal object of this invention to provide an improved lubricating system for an outboard motor.
It is a further object of this invention to provide an oil reservoir arrangement for the internal combustion engine of an outboard motor that prevents spillage of the lubricant from the reservoir when the engine is oriented in an abnormal condition.